Extraction of Tantalum Powder via the Magnesium Reduction of Tantalum Pentoxide
Round 1
Reviewer 1 Report
REVIEW THE MANUSCRIPT
“Extraction of tantalum powder by magnesium reduction of tantalum pentoxide”. Authors: Seon-Min Hwang, Jei Pil Wang, Dong-Won Lee
Judging by the works cited, the authors are not well informed with research in this area. This leads to an erroneous interpretation of the experimental results.
1) The mechanism proposed by the authors for the formation of metal particles (lines 88-92 and Fig. 4) contradicts the research carried out in the work:
Müller R., Bobeth M., Brumm H. et al. Kinetics of nanoscale structure development during Mg-vapour reduction of tantalum oxide / Int. J. Mat. Res. 2007. V.98. № 11. P. 1138 – 1145, and the experimental data of the works:
V. M. Orlov, M. V. Kryzhanov, and Academician V. T. Kalinnikov Magnesium Reduction of Tantalum Oxide Compounds / Doklady Chemistry, 2014, Vol. 457, Part 2, pp. 160–163. DOI: 10.1134/S0012500814080035
V. M. Orlov, M. V. Kryzhanov Production of Tantalum Powders by the Magnesium Reduction of Tantalates / Russian Metallurgy (Metally), Vol. 2015, No. 7, pp. 590–593.
DOI: 10.1134/S0036029515070101
V.M. Orlov, M.V. Kryzhanov, A.I. Knyazeva Tantalum Powders with a Mesoporous Structure / Protection of metals and physical chemistry of surfaces. 2016. Vol. 52. No. 5. P. 814-818. DOI: 10.1134/S207020511605018X
They show that the reduction occurs in the whole volume of the pentoxide particle with the formation after removing of magnesium oxide of a sponge-like particle of tantalum powder.
2) By this, the data in Table 1 is interpreted incorrectly (lines 147-150). The authors explain the increased oxygen content in the powders obtained by reduction at temperatures of 1073 and 1123 K by incomplete reduction.
According to Fig. 9, the estimated content of the Ta2O oxide phase in these powders is about 50 and 5%, respectively. Ta2O oxide contains 4.2% oxygen. Thus, the oxygen content inside the powders is about 2 and 0.2%. The rest of the oxygen is in the passive film on the surface of the powder. The high content of oxygen in powders obtained by reduction at temperatures of 1073 and 1123 K is a consequence of their large specific surface. Authors can verify this by measuring the specific surface area of powders using the BET method.
The remaining comments.
Line 23. Tantalum belongs to the group of rare metals and not rare earth metals.
Lines 26, 27. It is used to manufacture capacitors not because of the high electrical conductivity of the metal, but because of the good dielectric properties of the anodic oxide.
Line 35. Sodium cannot be used to reduction Ta2O5. In work [8], referred to by the authors, it is used to reduction tantalum fluoride salt.
The article may be published after processing taking into account the comments made.
Author Response
Dear Reviewers in MDPI
Thank you very much for your detail and helpful indication and even for upgrade on our articles.
We have tried to correct the text carefully as your indications.
Please see the final version in function of “Track-Changes” in MS-Word.
Responses on Reviewer I.
1) The mechanism proposed by the authors for the formation of metal particles (lines 88-92 and Fig. 4) contradicts the research carried out in the work…..
The reduction on whole volume were studied in the previous work shown in your providing references. But they used not tantalum oxide but tantalate as raw material.
So, because the initial materials are different with us, we think the reduction behavior is also a little different. Moreover Ta2O phase was found partially in XRD study in Fig. 10
Therefore we wanted to describe that the Ta2O appeared as just intermediated phase.
Above our opinion and related references which you provided were added in Line 103~109 and Line 220, respectively.
2) By this, the data in Table 1 is interpreted incorrectly (lines 147-150). The authors explain the increased oxygen content in the powders obtained by reduction at temperatures of 1073 and 1123 K by incomplete reduction…..
After seeing your indication, we were shy that our discussion was not correct.
Therefore the discussion related with it was corrected in Line 169~174.
And the SEM microstructure was added newly in Fig. 8, a) (Line 143)
and the result of BET surface areas were also added newly in Table 1. (Line 180)
3) Line 23. Tantalum belongs to the group of rare metals and not rare earth metals.
It was change as your comment (Line 23)
4) Lines 26, 27. It is used to manufacture capacitors not because of the high electrical conductivity of the metal, but because of the good dielectric properties of the anodic oxide.
It was change as your comment (Line 26)
5) Line 35. Sodium cannot be used to reduction Ta2O5. In work [8], referred to by the authors, it is used to reduction tantalum fluoride salt.
“Sodium” was deleted as your comment (Line 39)
2019. 1. 17
Correspondence: Dong-Won Lee, Korea Institute of Materials Science (KIMS)
Correspondence: Jei-Pil Wang, Pukyoung National University (PKNU)
Author Response File: 
Author Response.docx
Reviewer 2 Report
This paper ingored the previous studies, and they were not compared with this work.
There is no progressive findings from the early works.
Comments for author File: 
Comments.pdf
Author Response
Dear Reviewers in MDPI
Thank you very much for your detail and helpful indication and even for upgrade on our articles.
We have tried to correct the text carefully as your indications.
Please see the final version in function of “Track-Changes” in MS-Word.
Responses on Reviewer II.
Main indication :
This paper reports the reduction of Ta2O5 powder by Mg vapor. However, this reaction was previously studied although it was not industrially applied as far as the reviewer knows. The literature survey is lacking…..
We added the text on the literature survey (Line 35~38, Line 45~48 )
and also added new 3 references among your provided literatures.
(Line 203, 209 and Line 220)
Additional indications :
1. Introduction; Magnesium reduction is a main issue, so the application of Mg in the other oxides such as TiO2 and Nb2O5 should be reviewed. Some merits and demerits can be summarized from the previous works on these oxides, and some topics can be deduced. The current production method using K2TaF7 and Na should be stated.
We tried to add the merits and demerit of out magnesium reduction (Line 41-45).
The commercial process with K2TaF7 and Na was introduced (Line 35-38)
2. Experimental; Because the liquid Mg is exposed to the whole reactor, most of Mg vapor will escape out of Mg holder without any interaction with Ta2O5…..
It was change (and added) as your comment (Line 44~45, 57~59)
3. In Fig.1 there is no temperature measurement system.
Fig 1 was newly modified with T/C line as your comment (Line 61)
.
4. The material used for sample holders are not shown. The sources of Ta2O5 and Mg as raw materials are unknown, as well as its purity, particle size etc. They are important information to examine the purity and morphology of the obtained Ta powder.
It was corrected as your comment (Line 54, 81)
5. In Fig.3 and 5, ICDD card numbers are probably shown as reference. However their original papers should be called. The title of x-axis should be “diffraction angle”, not 2 theta.
It was corrected as your comment (Line 86, 127)
6.Line 79, the reference of phase diagram should be shown.
Fig 4. was newly added as your comment (Line 96)
7. Line 83, the excess amount of Mg should be removed as well as MgO.
It was corrected as your comment (Line 92~93)
8. Line 85, 87 and 99,100, the numerical values of free energy should be based on the valid reference.
Free energy changes were found by soft-ware the HSC 5.1 (Line 99)
9. The vapor pressure of Mg can be shown for the readers’ understandings. It should be stated whether the reactant Mg remained in the original position or all the charged Mg evaporated completely after 10h.
It was corrected as your comment (Line 57~59)
10. In Ta-O binary phase diagram, Ta2O may be recognized as a stable phase. This can be stated.
Ta2O phase could not be found in Ta-O phase diagram.
But we found the below JCPDS information of XRD peaks. Therefore we mentioned Ta2O shortly as just intermediated phase.
JCPDS No. 74-2305 :
- 1st peak 2q = 38.1 (999)
- 2nd peak 2q = 54.9 (132)
- 3rd peak 2q = 60.9 (247)
11. Line.127 Ref.[9] should come just after the equation.
It was corrected as your comment (Line 149)
12. Line 128-129 “B is ….”should be revised.
It was corrected as your comment (Line 150~152)
13. Fig.8 shows that the coexistence of Ta2O refined the particles size. Is it right?
In Fig 8, crystallite sizes were measured in the splitted XRD profile of only Ta Phase.
So, in Fig 8, there is no an affect of coexistence of Ta2O on refinement.
14. Line.151 1.25 wt% looks better than 1.35 wt%. The higher temperature seems better than 1173 K. Because this comparison was taken in the conclusion, the reason of optimization should be stated by accepting the difference. Thermal energy saving might be one of the reason. If so, the shorter period for reaction should be studied.
It was corrected as your comment (Line 175~176)
15. Table. 1. High nitrogen contamination (1.20%) at 1073K should be explained.
Nitrogen can be absorbed on the surface at room temperature when tantalum powder is taken out in air atmosphere. And it should be fully removed during N/O analysis but it seemed to be detected in analyzer without full removing, in particular it was significant in fine powder produced at low 1,073K.
Nitrogen content is not important topic so the result of nitrogen contents was deleted. (Line 180)
16. Line 164 There is no evaluation on the obtained oxygen level of 1.3% and the particle size of 11.5nm to 24.7nm.
It was corrected as expression “1.25~1.35 wt.%” (Line 190)
The evaluation on “11.5~24.7 nm” is in Line 153
English expression can be brushed up at least at the parts listed below.
1. line 17,35,39, 63, 159“And”=> deleted.
2. l.18 “to 1,173K where”=> “to be 1,173K because”
3. l.19 “near”=> “about”
4. l.27 “Therefore, in parts or”?
5. l.78 “by”=> “in the”or “at the”
6. l.135 “In next step, it was required to”.Who required?
7. l.144 “until”=> “to”
All was changed as your comments.
Thank you very much again for your beneficial and helpful indications to up-grade our submitting article.
2019. 1. 17
Correspondence: Dong-Won Lee, Korea Institute of Materials Science (KIMS)
Correspondence: Jei-Pil Wang, Pukyoung National University (PKNU)
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
In my opinion, the formation of a particle of tantalum powder during the recovery of pentoxide occurs according to the work Müller R., Bobeth M., Brumm H. et al. // Int. J. Mater. Res. 2007. V. 98. P. 1138. Thanks to this mechanism, it was possible to significantly increase the specific surface of the powder during the recovery of magnesium tantalate. In your work, as I assumed, a powder with a large surface (21.81 m2/g) was obtained at a temperature of 1073 K. This surface is much larger than that which can be calculated from the external dimensions of the powder particles.
The reason for the insufficiently complete reduction In your studies at a temperature of 1073 K is most likely a deficiency of magnesium due to the low rate of evaporation at atmospheric pressure of argon in the reactor.
I wish you success in your future work.
Author Response
Responses on Reviewer I.
In my opinion, the formation of a particle of tantalum powder during the recovery of pentoxide occurs according to the work Müller R., Bobeth M., Brumm H. et al. // Int. J. Mater. Res. 2007. V. 98. P. 1138. Thanks to this mechanism, it was possible to significantly increase the specific surface of the powder during the recovery of magnesium tantalate. In your work, as I assumed, a powder with a large surface (21.81 m2/g) was obtained at a temperature of 1073 K. This surface is much larger than that which can be calculated from the external dimensions of the powder particles.
I have experienced that BET surface area in case of nano-particle can be very largely fluctuated according to the dispersed degree. So you can understand I think it is some difficult to compare directly BET value with that calculated by particle dimension.
The reason for the insufficiently complete reduction in your studies at a temperature of 1073 K is most likely a deficiency of magnesium due to the low rate of evaporation at atmospheric pressure of argon in the reactor.
As you pointed out, it was corrected in text to “the effect of low reduction driving force as well as magnesium partial pressure”
: Line 166-167.
Author Response File: Author Response.docx
Reviewer 2 Report
Reviewer's comments
When the reviewer tried to find the related references on magnesium reduction of tantalum oxide,
23 papers could be listed as the below-listed papers. Many researchers have worked under the same topics studied in this paper, at least ref.1,4,5,6,7,8,13,14,15,17,18,20,21 are strongly related with this study concerning magneciothermic reduction of Ta2O5. They are the same of this paper. All these papers should be examined deeply before starting this work. The authors should not neglect to read them. Their activies should be summarized with several comments, and the advantages of this methods should be stated from the viewpoints of histrical developmet of tantalum power formation. Most important point is to deduce something new from the previous works for new study such as this paper.
As the reviewer found, there is only one thing different from the other works, and it is the existence of Ta2O. However, this paper did not take this finding as a special issue. Why could the authors find Ta2O, and what is the nature of Ta2O? How can we synthesis Ta2O in the way to metallic Ta?
Most of this work is a trace of the previous studies. The reviewer have to judge that this paper is not original work and not worth for new publication as the seconday publication. This paper should submit as a new paper considering the formation of intermediate phase Ta2O. The experimental data in this paper can be partially used under such new concept.
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1.Kinetics of nanoscale structure development during Mg-vapour reduction of tantalum oxide
Mueller, R.; Bobeth, M.; Brumm, H.; et al.
INTERNATIONAL JOURNAL OF MATERIALS RESEARCH 98 11 (2007) 1138-1145
2.Niobium and Tantalum Powders from Lithium Niobate and Lithium Tantalate Production Waste
Orlov, V. M.; Kiselev, E. N.; Kryzhanov, M. V.
THEORETICAL FOUNDATIONS OF CHEMICAL ENGINEERING 52 (4) 634-637
DOI: 10.1134/S004057951804022X
3.A new technology platform for the production of electronic grade tantalum nanopowders from tantalum scrap sources
Lessard, Joseph D.; Shekhter, Leonid N.; Gribbin, Daniel G.; et al.
INTERNATIONAL JOURNAL OF REFRACTORY METALS & HARD MATERIALS, 48 (2015) 408-413
DOI: 10.1016/j.ijrmhm.2014.09.027
4.Thermodynamic modeling of magnesiothermic reduction of niobium and tantalum from pentoxides
Kryzhanov, M. V.; Orlov, V. M.; Sukhorukov, V. V.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY, 83 (3) (2010) 379-383
DOI: 10.1134/S107042721003002X
5.Magnesium-mic reduction of tantalum oxide by self-propagating high-temperature synthesis
Orlov, V. M.; Kryzhanov, M. V.
Russ. Metall. 5 (2010) 384-388
6.Preparation of capacitor powders from the wastes of tantalum capacitor production
Orlov, V.M.; Kiselev, E.N.
Khim. Tekhnol. 11 (2013) 682-687
7.Magnesium reduction of tantalum oxide compounds
Orlov, V. M.; Kryzhanov, M. V.; Kalinnikov, V. T.
DOKLADY CHEMISTRY, 457 (2) (2014) 160-163
DOI: 10.1134/S0012500814080035
8.Deoxidation of the Tantalum Powder Produced by Self-Propagating High-Temperature Synthesis
Orlov, V. M.; Kryzhanov, M. V.
RUSSIAN METALLURGY 3 (2014) 191-194
9.X-ray diffraction study of sodium metal reduction tantalum powders
Orlov, V. M.; Osaulenko, R. N.; Malyshevsky, D. N.; et al.
INORGANIC MATERIALS, 50 1 (2014) 46-51
10.Production of tantalum nanopowders by the magnesiothermic reduction of tantalates
Orlov, V.M.; Kryzhanov, M.V.
Metally, 4 (2015) 93-97
11.Magnesium-vapor reduction of niobium oxide compounds
Orlov, V. M.; Kryzhanov, M. V.; Kalinnikov, V. T.
DOKLADY CHEMISTRY, 465 (1) (2015) 257-260
DOI: 10.1134/S0012500815110026
12.Influence of the Precursor Composition and the Reduction Conditions on the Characteristics of Magnesium-Thermic Niobium Powders
Orlov, V. M.; Kryzhanov, M. V.
RUSSIAN METALLURGY 7 596-601 (2016)
DOI: 10.1134/S0036029516070107
13.X-Ray Diffraction Study of Magnesiothermic Tantalum Powders
Orlov, V. M.; Osaulenko, R. N.; Kryzhanov, M. V.; et al.
INORGANIC MATERIALS 53 4 (2017) 391-396
DOI: 10.1134/S0020168517040136
14.The role of the reaction medium in the self propagating high temperature synthesis of nanosized tantalum powder
Nersisyan, HH; Lee, JH; Lee, SI; Won, CW
COMBUSTION AND FLAME 135 4 539-545 (2003)
DOI: 10.1016/j.combustflame.2003.08.006
15.Method for producing tantalum/ niobium metal powder by the reduction of their oxides with gaseous magnesium
Patent Number: 6 171363
Shekhter, L. N.; Tripp, T. B.; Lanin, L. L.
US Patent Published: 2001
16.Tantalum powder production by magnesiothermic reduction of TaCl5 through an electronically mediated reaction (EMR)
Park, I; Okabe, TH; Waseda, Y
JOURNAL OF ALLOYS AND COMPOUNDS 280 1-2 (1998) 265-272
17.Production of tantalum powder by magnesiothermic reduction of feed preform
Okabe, TH; Sato, N; Mitsuda, Y; Ono, C
MATERIALS TRANSACTIONS 44 12 (2003) 2646-2653
DOI: 10.2320/matertrans.44.2646
18.Production of niobium powder by magnesiothermic reduction of feed preform
Okabe, TH; Iwata, S; Imagunbai, M; et al.
ISIJ INTERNATIONAL 43 12 (2003) 1882-1889
DOI: 10.2355/isijinternational.43.1882
19.Production of fine tantalum powder by electrochemical method
Yuan, Boyan; Okabe, Toru H.
MATERIALS TRANSACTIONS 48 10 (2007) 2687-2694
DOI: 10.2320/matertrans.M-MRA2007876
20.Production of fine tantalum powder by preform reduction process using Mg-Ag alloy reductant
Yuan, Boyan; Okabe, Toru H.
JOURNAL OF ALLOYS AND COMPOUNDS 443 1-2 (2007) 71-80
DOI: 10.1016/j.jallcom.2006.10.004
21.Combustion synthesis-derived tantalum powder for solid-electrolyte capacitors
Won, H. I.; Nersisyan, H. H.; Won, C. W.
JOURNAL OF ALLOYS AND COMPOUNDS 478 1-2 (2009) 716-720
DOI: 10.1016/j.jallcom.2008.11.140
22.Tantalum and niobium powder preparation from their oxides by calciothermic reduction in the molten CaCl2
Baba, M; Ono, Y; Suzuki, RO
JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 66 2-4 (2005) 466-470
DOI: 10.1016/j.jpcs.2004.06.042
23.Formation of broccoli-like morphology of tantalum powder
Suzuki, RO; Baba, M; Ono, Y; et al.
JOURNAL OF ALLOYS AND COMPOUNDS 389 1-2 (2005) 310-316
DOI: 10.1016/j.jallcom.2004.08.016
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As the reviewer requested, Fig.4 was added. However there is no citation.
Author Response
Responses on Reviewer II.
When the reviewer tried to find the related references on magnesium reduction of tantalum oxide,
23 papers could be listed as the below-listed papers. Many researchers have worked under the same topics studied in this paper, at least ref.1,4,5,6,7,8,13,14,15,17,18,20,21 are strongly related with this study concerning magneciothermic reduction of Ta2O5. They are the same of this paper. All these papers should be examined deeply before starting this work. The authors should not neglect to read them. Their activies should be summarized with several comments, and the advantages of this methods should be stated from the viewpoints of histrical developmet of tantalum power formation. Most important point is to deduce something new from the previous works for new study such as this paper.
Thanks for your trial for up-grade of article in introduction part. We have surveyed again your providing literatures A~G at 1st review and 1~23 at 2nd review. We agree that among them, A, B, C, F, 1, 5, 8, had the strong similarity. So we tried to find a difference with them and corrected and added some texts in introduction region newly.
: Line 48~53
As the reviewer found, there is only one thing different from the other works, and it is the existence of Ta2O. However, this paper did not take this finding as a special issue. Why could the authors find Ta2O, and what is the nature of Ta2O? How can we synthesis Ta2O in the way to metallic Ta?
Most of this work is a trace of the previous studies. The reviewer have to judge that this paper is not original work and not worth for new publication as the seconday publication. This paper should submit as a new paper considering the formation of intermediate phase Ta2O. The experimental data in this paper can be partially used under such new concept.
The intermediate phase Ta2O appeared in sample reduced incompletely and disappeared in the more elevated temperatures in our study. When seeing ref. 9 your provided, we can knew Ta2O peaks are positioned similarly with this those of TaH and Ta2H. But we have believed so far our small peaks are Ta2O phase and it will be required more study to find a nature. Overall we agree our submitting paper is considerably similar with many previous works, but please understand that we have thought there is no previous case satisfied simultaneously all of 1) using Ta2O5 raw material, 2) using not preform but powder of raw powder, 3) changing reduction temperature and 4) no-using flux employed in our work.
As the reviewer requested, Fig.4 was added. However there is no citation.
It was added in text “by thermochemical software(FactSage 7.2)”
: Line 94
Thank you very much again for reviewing
Author Response File: Author Response.docx
